Seismic data representing a plurality of seismic channels is conventionally stored on magnetic tape for further data processing. In one such data processing operation, the information stored on the magnetic tape is used to modulate a cathode-ray tube so as to display the information on the face of the cathode-ray tube. Such display is photographically recorded by means of a conventional drum plotter. Rotation of the drum plotter past the face of the cathode-ray tube results in a seismic trace recording on the photographic material surrounding the drum plotter. In order to plot additional seismic trace recordings adjacent to previous recordings, the cathode-ray tube is mounted on a movable assembly which is automatically stepped laterally to the next seismic trace recording position. An illustration of such a data processing operation is set forth in FIG. 1 of the accompanying drawings to assist in an understanding of the prior art. For a more detailed description of such operation, reference may be had to U.S. Pat. Nos. 3,704,450; 3,714,663; and 3,886,526.
When the seismic information from the magnetic tape unit is applied to the H-axis input of the CRT, the direction of travel of the electron beam across the face of the CRT is modulated so as to produce a variable-amplitude photographic recording on the drum plotter. However, should this same seismic information be applied to the Z-axis input of the CRT, the brightness of the electron beam will be modulated as it travels across the face of the CRT so as to produce a variable-density seismic trace recording on the drum plotter.